[TCGC++] Add client codegen support for range requests

### Clear and concise description of the problem

Not sure exactly how we generate code for a service that supports range requests today, but I strongly suspect there are opportunities to do better/add intrinsic knowledge about range requests (and corresponding conditional requests) in our code generators.

For example, we could return a random access byte array/stream. With built-in caching. And know that subsequent GET requests should include conditionals that fail if the target resource has been modified since the first range was received.

### Checklist

- [x] Follow our [Code of Conduct](https://github.com/azure/typespec-azure/blob/main/CODE_OF_CONDUCT.md)
- [x] Check that this issue is about the Azure libraries for typespec. For feature request in the typespec language or core libraries file it in the [TypeSpec repo](https://github.com/Microsoft/TypeSpec/issues/new/choose)
- [x] Read the [docs](https://azure.github.io/typespec-azure/).
- [x] Check that there isn't already an issue that request the same feature to avoid creating a duplicate.

The issue does not identify a generator file, test, or entry point for range-request support. Start by locating how TCGC++ generates clients for range and conditional requests, then determine the intended API, caching behavior, and modification checks before defining completion criteria.

Written by the indexing model from the issue text.